The composite (plastic) intake manifold may crack near the thermostat housing and cause a coolant leak. Ford released an updated manifold that was reinforced to prevent a recurrence. No recall was issued for this problem but Ford did extend the warranty to seven years on some models from the date of purchase.
Car Problem Reports
Mercury Mountaineer Plastic Intake Manifold May Crack Causing Coolant Leak
Mercury Mountaineer Problem
Electrical & Lights Affected: 4.6L V8
Average Mileage: 121,402 mi (47,000 mi - 200,200 mi)
Visitor, 1999 Mercury Mountaineer, 76,220 mi
Driving down the road, pressed gas pedal and white smoke started coming out back. I pulled over and antifreeze was all over the inside of the engine and hood. Looked and intake manifold where thermostat is housed was completely cracked. It's been leaking for the past month causing antifreeze to cause the ignition coils in cylinder 7 and 8 to go bad. Now it's completely cracked. A shame ford never officially recalled this, poor design that is now costing consumers a hefty bill for a new intake manifold to replace something that wasn't manufactured right to begin with!
Visitor, 2002 Mercury Mountaineer, 148,000 mi
I'm purchasing a 2002 mercury mountaineer from a in house financing car dealership and after I drove it for bout a week I noticed the truck started running hot and I finally took it to the shop and they told me that the intake manifold is falling apart because its plastic and its getting to hot and they wanted to charge me around 700 dollars to get it fixed
Visitor, 2002 Mercury Mountaineer, 189,000 mi
This problem will cause water to leak into the cylinders and cause them to miss fire making you think there is a problem with the plugs and coils. The car will run horribly but if you look closer you will find that it is in dead the plastic piece under the thermostat housing. It is a real pain. I am still trying to get his fixed and I am sure it is going to cost me a lot of money because it is no longer under warranty.
Visitor, 2002 Mercury Mountaineer, 146,000 mi
cracked manifold thermostat housing. Tried to stop the leak with liquid weld--no good. As soon as the car heats up it breaks the welding.
Visitor, 2002 Mercury Mountaineer, 121,811 mi
Same problem as most others. Notice a miss in one of the cylinders. Took it to the garage to diagnose further. Reported to be the plastic piece of the intake manifold. Really???? A plastic piece on the motor of a car that is constantly heated to high temperatures? Nothing further needs to be said there..
Visitor, 2005 Mercury Mountaineer, 106,000 mi
engine overheating, coolant pooling at spark plugs, diagnosis: cracked intake manifold.. replaced intake manifold..
Visitor, 2006 Mercury Mountaineer, 141,000 mi
Cracked thermostat housing as in earlier posts, resulting in overheated engine however no previous engine problems. Replaced thermostat and housing for around $85 from Auto Zone, seems to have fixed the issue completely.
Visitor, 2002 Mercury Mountaineer
not fixed yet cause i cant afford to at this time
Visitor, 2005 Mercury Mountaineer, 81,000 mi
Manifold leaking. Causing coolant to leak into spark plugs which is shorting them out. Truck isn'r even paid for.
Visitor, 1999 Mercury Mountaineer, 150,000 mi
When idling my vehicle has a steady drip of "water" from the tailpipe